texts: What do the calendar rounds in Tomás Filsingers "Map of the Universe 2.000" mean?

texts:
Recently I did the Ravensburger puzzle "Map of the Universe 2.000 - Celestial Chart and Calendar Rounds" by Tomás Filsinger:

Tomás said the last time he visited this site in 2019, that he finished a new, improved map. I recognize some of the described features in the puzzle, e.g. the "60 galactic years since the big bang".
I am just trying to analyse the multiple rings of calendars, like the meaning of the blue and orange triangles, the tiny colored lines with squares (I think they are planets, but how do they relate to the calendar?), the red to blue-colored ring, why the grey (on the innermost ring) and yellow constellations (as part of the firmament), and the blue months and the grey months are shifted against another, why there are stars on the outer ring ... well almost most of what is going on in this exquisitely beautiful, but (at least for me) quite complex chart.
I asked the publisher, but he was not able to explain it.
If someone might be interested, I could send details of the map.
Perhaps Tomás is reading this, like in the other post, and could explain his map himself?
p.s.: I included a detail photo of the puzzle).
You can see several things here (from bottom to top, with my comments in parenthese; please forgive my choice of terms, I am a star map rookie):

grey triangles with the galactic years, divided in 12 steps (why?), and small diamonds with major events, but on another scale (10, 1.000, 2.150 years: why?). There must also be some kind of horizon, because there is the Southern Cross, and Alpha Centauri.
a dotted line, with a white dot for every 20 blue dots (dont know, must be something regarding planets, there is a tiny Venus on the right and the weekday is Friday).
4 lines with jovian planets (I think), and their movement over the year (I think).
a red dotted line, for Mars (I think).
the days of the respective month, with orange triangles (why are they pointing at the dotted lines?).
the months in different languages, with their meteor showers.
a white dotted line, for Venus (I think, text is "263 days as evening star").
another very tiny line (Mercury?)
days of week, in different languages, with some objects.
a band with a spectrum (which?), red to blue, here green, with missing lines (which?).
signs of the zodiac.
degrees of longitude, including hours of the day (why?).
sky map, with day of month ("16, "17", why?), moon phases, yellow dashed line (which?), ecliptic, celestial equator, and of course many objects and constellations.

And: how is it all connected to another ;-)
There are some more details, but these are the main constituents and corresponding questions. The booklet Tomás provided for downloading in the other post should help a bit, and if you refer me to other sources because this is all standard stuff, that would be fine for me.
Looking at my questions at the start of the post I already see that I answered some of my former questions myself, but much is left :-/


texts: What's the terminology of a meteor "ditch" when impact happens at an angle?

texts: When a meteor hit the surface of a planet, it creates an impact crater. When an meteor hit the surface of a planet at an angle, like it usually happens in the movies, what do you call the long "ditch" that is formed before the actual crater where the meteor came to rest?


texts: Shall we say now that Pluto is "larger than Mercury" ?

texts:
http://pluto.jhuapl.edu/News-Center/News-Article.php?page=20150717-3

"Scientists working with NASA’s New Horizons spacecraft have observed Pluto’s atmosphere as far as 1,000 miles (1,600 kilometers) above the surface of the planet, demonstrating that Pluto’s nitrogen-rich atmosphere is quite extended."

I note that conventional descriptions of the gas giants' sizes include mostly atmosphere.


texts: Do space objects stay in orbit once they get sucked in? Can they escape?

texts:
Think of my question with respect to 2020 CD$_3$ minimoon that's been recently discovered.
If an object gets caught into a planet's orbit, can it ever escape it?
Obviously it may escape on the first pass without making any full revolution.
But if one or two revolutions took place, can it ever escape the planet's orbit on its own momentum it came in with?


texts: Dark Flow: statistical limits on existence

texts:
Dark Flow has been thrown around as a term a lot lately, especially with the latest Planck results.

New Scientist reported last year that it was now statistically improbable, but the paper by Atrio Barandela mentioned in the article places doubt on the statistical significance of the dipole measurement by the Planck team.

I'd like to know what observational limits lie on it's existence as a physical phenomena (giant attractor/multiverse/new region of spacetime/other weirdness) and not just a statistical anomaly in the overall matter distribution, I.e. what future observations could prove or disprove this theory?


texts:
I was wondering how the researchers were able to minimize or neutralize confirmation bias regarding the data collected?

As I understand it, the algorithm pruned much of the data, which would make sense, since it would likely be useless noise. See for example the video Event Horizon Telescope Press Conference. First Image Of a Black Hole. at about 38:40.

  Five petabytes is a lot of data… The image you saw of course isn’t 5 petabytes in size, it’s a few hundred kilobytes, so our data analysis has to collapse this five petabytes of data into an imaget that’s more than a billion times smaller.

But apart from that, could certain features be misidentified as artifacts, and be thrown out in favour of preselecting what researchers expected to see?

The only reason I ask is that the image looks almost identical to simulated predictions from two years ago - which may raise a slight cause for alarm.

Thank you.

To follow up (based on answers section below):

In the first stage process - "common features" - are they like existing stamps of astronomical features (and image comparatives) that have been already observed in our universe (in both the visible and invisible spectrum and used for comparison)? And a second question - if we have never observed the earmarks of a black-hole before, how are we to use existing stamps of knowledge of astronomical features that we have seen to assess and validate an as of yet unknown (which would seem to directly impact what artifacts are preserved and what artifacts are thrown out and discarded)?


texts: Which redshift is used to determine the Hubbleconstant?

texts:
I think they measure cosmological redshift to use in the Law of Hubble-Lemaître together with the distance to calculate $H_0$. Is this correct, or do they use Doppler shift (too)?
$H_0$ indicates how fast the universe is expanding, so I find it logical that we measure cosmological redshift. But the galaxies are receding (due to the Hubble Flow) away from us, so do they gain an additional Doppler shift?


texts:
This is a naive question. I have a temperature map of radio emission at 1420 MHz, in Kelvin. I want to extract the flux density (in Janskys) from an extended region of this map.
Is the flux density ($S_{\nu}$) from this region equal to
$$ S_{\nu} = \frac{2\nu^2 k_B T_{\text{mean}}}{c^2} \times A$$
where $\nu$ is the frequency of my map, $k_B$ is the Boltzmann constant, $T_{\text{mean}}$ is the mean value of the temperature inside my region, $c$ is the speed of light and $A$ is the area of my region in steradians?


texts:
Moon can be fully eclipsed by the virtue of being fairly close to Earth. Any body distant enough will not be eclipsed fully, Earth's disc not fully covering Sun's disc. How's that for anything at the L2 point? Will it be lit by Sun's corona or will it bask in deep shadow of Earth?

Bonus question: if Umbra does reach there, how large a body could remain fully shaded at L2? What's the Umbra's radius there?


texts: How was Cruithne's orbital time calculated?

texts:
How was it determined that Cruithne takes 770 years to complete its cycle with Earth? Janus and Epimetheus were disovered long enough ago, and have short enough cycle times, that we've had time to directly observe their 8 year cycle more than 6 times over. But Cruithne was only discovered 30-ish years ago, so certainly it's cycle time wasn't determined by simple observation.

So what method was used to arrive at this 770 year number?


texts: Difference of Gas Giant Planet and Ice Giant?

texts: What is the Difference of or the Structure of a GAS PLANET AND AN ICE GIANT Why they called ICE GIANTS like Neptune and Uranus. Do they have a similarity ?


texts: Is it possible to know if a planet is located in the Habitable Zone knowing it's properties?

texts:
Is there an equation that can give me the possibile distance of the planet from his star knowing planet's temperature (or other datas)?

I found this method for calculating the Habitable Zone but it's based only on star's properties.


texts: How do scientists know there are about 300 billion stars in a galaxy and there are about 100 billion galaxies?

texts: Just to think about this is mind boggling. But how do scientist get these numbers? What technology/system/theory do they they use?


texts:
I know black dwarf stars do not exist yet, and that they are what white dwarfs end up after a long time. The question is really simple: would it be possible to have a binary system in which one of the two is a black dwarf, and the other companion star is dumping mass on the black dwarf, causing the black dwarf to supernova? I guess based on the timescales, the maximal initial mass of the second object could be calculated to see if it is possible that one object is at the black dwarf stage and the other still a giant. Or is the timescale on which the star goes from white dwarf to black dwarf big enough that it will never reach the black dwarf stage while the other one is still an AGB star?

Second part: If not possible that one is black dwarf and the other AGB star, is it possible if the companion is a brown dwarf, that they are close binary, and that a brown dwarf would dump mass on a black dwarf? This would need the binary system to be a very close binary system at this stage of the system.

Third part of the question: would the spectrum of the supernova be any different from the normal one with a white dwarf and a companion AGB star? I guess the spectral lines would be different, since the companion would have to be a very low-mass AGB star, since that companion would be about 20billion years or so, when the black dwarf star becomes a black dwarf.


texts: What is the radiant intensity of the celestial sphere?

texts:
Specifically, excluding the Sun and the Moon:
How much energy, as light and other frequencies reaches a point in space on the average, if you add up all the sources like distant stars, the Milky Way, distant galaxies, nebulae etc.? How much brighter is the space than "perfect blackness" on the average?

Say, we've developed a magical solar battery that has 100% efficiency, can absorb all electromagnetic frequencies, is spherical, fully omnidirectional and has $1 m^2$ of cross-section surface (56cm radius);  we sent it out halfway to Proxima Centauri and we measure how much power it produces - how many watts we'd get out of the battery utilizing all the starlight available?

Note: If "all frequencies" is not easily obtainable, the luminous counterpart to radiant values will be okay (only taking visible spectrum into account).


texts: Where can one find a reliable list of black holes that have been discovered/observed so far, directly or indirectly, along with their properties, like mass, spin, etc.?


texts: Why does the sun appear 13x bigger through diffraction in Voyager 1 image from 1990, but not from Earth?

texts:
The sun in the Voyager 1 photo here from 1990 appears 13x bigger than its diameter, diffraction of course. On Earth, photographs of the sun do not make it appear 13x bigger. Why?

A description of the photo from jpl.nasa.gov,

  "The wide-angle was taken with the camera's darkest filter (a methane
  absorption band), and the shortest possible exposure (5 thousandths of
  a second) to avoid saturating the camera's vidicon tube with scattered
  sunlight. "


texts: Conundrum involving distance to object, universal expansion, age of universe, etc

texts:
I was recently reading about a galaxy or quasar (not sure which, so lets just say quasar) where the estimated distance to this thing was some very significant fraction of the age of the universe.  What I mean is this:  I can't recall the exact particulars, but assuming for argument's sake that the age of the universe is 13.8 billion years old, this thing was like 13 billion light years away.  (Again, some detail here might be slightly off; the thing might have been estimated at 12 billion light years away - so focus on the general principle I am layout out here, not any particulars).

What I don't understand is this.  If the thing is 13 billion light years away, then the light reaching my eyes as I look at it now took 13 billion years to get to me.  Yet the age of the universe is 13.8 billion years old (again if I'm slightly wrong in some of these numbers, just accept them for now for argument's sake).  It means the light must have left this object when the universe was much "smaller" or more compact, and things were much closer together.  Which means the light should have passed my position a long time ago if I have been either "moving" or "expanding" (or some combination) away from the object at anything except some rather large percentage of the speed of light.

To try to boil this down, or restate it in simpler terms:  1) either it seems I am moving/expanding/red-shifting away from this object at some significant fraction of the speed of light (haven't done the numbers, but might be 80% or 90% or so) and have been for a while, or 2) something is "off" (the age of the universe, or the distance of this object).

or 3) there is something I'm not understanding.  Which is why I came here.

I have never seen it stated that we are "expanding" or "redshifting" or [insert whatever term you like] at some significant fraction of the speed of light; I have only ever seen it stated that for some brief period of time after the big bang the universe could have (or did) expand faster than light, but again that was for like less than a second if memory serves.

At any rate, anyone care to explain?

Thanks.


texts: What skills would a software developer need to get a job in space research or exploration organization?

texts: I am in the field of software programming. What skills should I brush up and gear up to get a job in space exploration and the observatory industry? What are various job profiles in terms of software development in this field?


texts: How do we convert other waves of the EMS to visible light?

texts: So I just had a quick question and I was wondering how we convert other waves of the electromagnetic spectrum to visible light waves. For example we use X-ray's or radio waves to see things in space like nebulae that we wouldn't normally be able to see with just visible light waves. But how do we convert those waves to visible light so we can actually see them.  I don't know if I'm staying this right but another example that just came to me is pictures of the Sun we see that was taken with radio waves, we see them,  which must mean that they were covered into visible light some how, so I was just wondering how, thanks in return =)


texts: For getting into a PhD program for observational astronomy,  is physics major and data science minor enough?


texts: What would I see with a telescope of 70mm aperture , 300mm focal length and maximum magnification of 150x

texts: What would I be able to see with 70mm aperture telescope with 300mm focal length with maximum magnification of 150 x?


texts: Do lower mass stars consume more hydrogen than higher mass stars?

texts: If I understand correctly, red dwarfs consume all of their hydrogen and will eventually shrink into helium white dwarfs, whereas the higher mass stars will consume a fair amount of their hydrogen fuel, not necessarily all of it. Correct me if I'm wrong.


texts: Arago Spot in the Shadows of Celestial Bodies

texts:
Recently, I've watched this video by Veritasium describing Poisson's Spot, or the Arago Spot. It is explained in the video that near circular (or spherical) objects can produce this optical effect, given that there aren't many obstructions about the circumference of the object to diffuse and scatter the light and the light producing the shadow is more or less in phase.

My question is, Are Arago Spots possible/Have Arago Spots been observed in the solar shadows of any celestial bodies?


texts: If objects don't move when the universe expands, how can the expansion result in redshift?

texts:
I am approaching this topic from a layman's perspective and view this as a logic puzzle, but when someone tries to get me to accept the logic, I'm never convinced by their arguments.

According to the wiki page on the expanding universe, the universe is expanding (which is how we see redshifted light from distant galaxies), however this expansion does not result in the movement of objects across space away from each other. Instead, this expansion is the formation of new space such that all of the objects in space maintain a static relationship with space.

This should mean, that as light produced by a distant light source that is expanding away from us, it is not moving away from the photon. The photon then travels across space, and this trip takes longer as a result of the expansion, but once the photon is in space near to Earth, the earth is not moving away from the light. By the time the light is at the same distance from the telescope as a flashlight held in front of the telescope, the telescope is not moving away from the photon any more than it is moving away from the photon produced by the flashlight.

So, IF the expansion is not the result of motion across space, HOW do we show redshift??????

Another comment, laymans perspective
The whole reason it can make sense that objects far enough away can expand away from us FASTER than the speed of light (which is the reason why telescopes can't see further) is that these objects are not moving across space to achieve this expansion.

Another comment in reference to the Raisin Cake.
understanding the expanding universe as a raisin cake swelling, therefore the actual cake that is in contact with any raisin stays in contact with that raisin,, the raisins do not move through the cake,,, APART. BUT, in space, the raisins actually ARE moving through the cake. Also, the PHOTON that travels across space from the distant light source to the telescope, travels across space. additionally, it's NOT useful to think of this transaction of energy in a raisin cake, because the raisins DO travel across space away from each-other as the cake swells, but this is NOT how we can possibly understand objects in space expanding away from us on Earth faster than the speed of light.


texts: Is it possible to figure out your location in the Milky Way if you are suddenly wormholed to a random, distant location in the galaxy?

texts:
If you were flying along in your spacecraft somewhere in our solar system and then a large, stable wormhole suddenly opened and you flew into it and were whisked away to some distant location in the galaxy, would you be able to figure out where you were?

Obviously, a large stable wormhole is exceedingly unlikely, and then there's the matter of the power of your onboard computer and telescope(s). But all that aside, I'm wondering if it would be even theoretically possible to figure out where you were, since the constellations would probably be unrecognizable and you wouldn't have an understandable flight path.


texts: Does Gravitational Time Dilation stack on top of Time Dilation caused by Velocity?

texts:
Using 1 CM from the Event Horizon of Super Massive Black Hole, SGR A, as the reference point. The particles within the accretion disk are traveling at extreme high speeds.  Assume this speed increases as the particles orbit closer and closer to the EH.

Are the particles within the accretion disk of Super Massive BH SGR A subject to time dilation both from 1) the gravitational field of SGR A at 1 cm from Event Horizon ...and 2) from the the acceleration of the particles traveling around the BH as they approach the EH?

Does the acceleration of particles act as an interference to the affects of the gravitational time dilation?  And if not, or if these two types of time dilation affect the time intervals for this group of particles,  When would an observer 1 light year from the EH see the particles enter the EH?  A) Before Impacting the EH, B) After impacting the EH,  or C) Never?


texts: Would a 1000 km telescope be able to resolve microscopic detail?

texts: I have calculated that a 100m telescope can resolve 16m on the moon. Does that mean a 1000km telescope is 10000x better and can resolve 1.6 mm objects on the moon and even smaller closer? Or is there some limit to using a telescope as a microscope?


texts: How can exoplanet moons be detected? Are there current methods to differentiate exoplanets with moons and exoplanets without moons? Or, are only the combined masses of the exoplanet and its moons detectable?


texts:
Lyman-$\alpha$ line in galaxies is notably known to show a double peaked profile, mainly due to its scattering in a moving medium, see e.g., the very recent Matthee et al. 2021, The X-SHOOTER Lyman-α survey at z=2 (XLS-z2) I: the panchromatic spectrum of typical Lyman-α emitters.
Reading through some literature I learned that most of the time the blue peak is reduced and the red one is enhanced because of the presence of outflowing medium, commonly present in star-forming galaxies. The peak separation is of the order of a few hundreds of $\rm km ~s^{-1}$. In case of inflowing medium (rarer) the situation is inverted.
I have in hands a spectrum of a galaxies with a Lyman-$\alpha$ absorbed at the systemic redshift and with a narrow component blueshifted by $>1000 ~\rm km ~s^{-1}$, whit no red peak. Is there any known mechanism that could explain this?


texts: Sky view from Stellarium software vs. Sky view with naked eye

texts:
I'm slowly starting to interest in astronomy. Currently I'm enjoying in stargazing but unfortunately place where I live is very light polluted.
I'm planing my vacation in a couple of months and one of the attractive places on my list is Tenerife because I can combine both star-gazing and going to the beaches. As per my research, base of Mountain El Teide is perfect for star-gazing so I tried to simulate El Teide location and date in the Stellarium software to see what I can expect. Based on the light pollution index (2) which Stellarium picked for me based on the location I got following picture:

Full resolution image
My question is: How this rendered picture will match my naked eye in the reality at the same location and time (we can assume that there will not be any clouds and that I'll be stargazing when moon is couple of days from New Moon phase). Can I expect something like this or even something better?
I'm aware of all the tips which can maximize my experience but I'm trying to just be sure that El Teide will not disappoint me. I really want have great star gazing-experience and try to see Milky way and much stars as possible because I don't have that luxury in the country where I live.
Any personal star gazing experience from Tenerife location is more than welcome. For my first time I'll plan to not use any equipment (except maybe binoculars)
Btw, there are stellarium settings used for picture that I attached (I assume that this is closest what you can see with naked eye).


texts: Could the earth's atmosphere have been partially stripped by a passing rogue planet?

texts:
I am involved in the fight between palaeontologists and aerodynamicists on the theoretical flight capabilities of the largest pterosaurs (who reached their climax in the Cretaceous and then disappeared at the K/T extinction event).

Is it possible that the earth's atmosphere was reduced at this time by a passing rogue planet or other sufficiently large body?

If so, the atmosphere would have been thicker.

Using the principle of Occam's razor, this one single hypothesis solves the problem of flight in the Mesozoic; the problem of how the dinosaurs could carry such weight; why they all had tails that would be much more use in a thick medium such as water...

The K/T extinction has attracted too many theories about what was 'added' to life on earth such as the comet/asteroid/Deccan Traps theories etc. No-one has looked at what might have been taken away from earth to cause the same effect!

If the earth's atmosphere had been much thicker (far higher pressure/density at the surface) the dinosaurs would have had a much easier time. Losing a huge amount of their atmosphere would kill them off because their 'effective weight' would have been doubled almost overnight.


texts: In the 1950's how were radio-astrometric positions with portable dishes so precise they could be assigned to their dim optical counterparts (Quasars)?

texts:
In my question Why are quasars so far away that they couldn't be optically resolved in the 1950's? I included the following short paragraph, but then added strikethrough to the second sentence and added a parenthetical based on @DavidTonhofer's comment.

So today instead of "quasi-stellar" we might simply say "unresolved". The light is star-like because the light from galaxies has a strong stellar component. (this second sentence is argued against in comments)

I then read further and found this short but informative historical account in University of Manchester's Jodrell Bank Centre for Astrophysics page The MKI and the discovery of Quasars:

Initially the radio sources were observed with the telescopes relativly close together. In this case the fringe pattern is very broad and greater than the typical angular size of radio sources so virtually all are observed to give fringes. However as the telescopes are moved apart, the fringe spaceing becomes finer and the fringes from many of the radio sources first reduced in amplitude and then disappeared. The separation of the telescopes when the fringes from each source reduced in amplitude (and the wavelength of the radio waves observed) allowed the angular size of the radio sources to be found.
To the surprise of the astronomers quite a number were found to have exceedingly small angular sizes - so small in fact that their images on a photographic plate would look like the images of stars. Much work then went into finding the precise location of these objects and finally it was possible to obtain their spectra. They were nothing like the spectra of stars or galaxies and remained a puzzle for some time. Finally it was realised that the reason that the spectra were so different was that the objects were so far away that their light was greatly red shifted. They were at very great distances away from us and so it was not surprising that their images were so small!
Because their images looked liked those of stars they were called Quasi-Stellar-Objects or QUASARS for short.

Question: In the late 1950's how were astrometric positions of these radio sources made so precisely that they could be assigned unambiguously to dim, star-like spots on photographic emulsions?

The 25ft Transportable Radio Telescope


texts: Will all galaxies eventually become elliptical galaxies?

texts: According to the Wikipedia article Elliptical galaxy, elliptical galaxies have a sparse interstellar medium. I know that probably sometimes two spiral galaxies collide then exponentially approach the state of being an elliptical galaxy. For a spiral galaxy that will never collide because if it hasn't collided before all the other galaxies went past its cosmic horizon, I wonder whether its interstellar medium will slowly get thinner until it's so thin that stars are no longer confined to the plane of the galaxy by friction and then as soon as a few of them start to go slightly outside the plane, they will bring with them their gravitational field causing stars to go further outside the plane and then after it gets wide enough, the interstellar medium will be even faster to get consumed by stars moving in random directions.


texts: Can a black hole reach a limit where it can no longer attract more matter? If so, what happens with that black hole? Does the black hole die? Does the black hole decrease its size?


texts: Name for pre-supergiant main sequence stars

texts:
The massive main-sequence stars which turn into supergiants--do they typically have special terminology for their classifications as do the less massive ones (which may be, e.g., "yellow dwarf" or "red dwarf")? Just "non-dwarf main sequence" or?

(I'm quite a novice, so pardon me if my premises are wrong too. Just trying to get a sense of some of the broad categories.)


texts: which pulsar has the longest spin period so far?

texts:
Vela X-1 has a 283s spin period, while this one may have a 2.7hr spin period.
However neither of them is included in ATNF catalog.
They are not included in $p-\dot{p}$ diagram either. The longest period is just about 10s in this diagram.

My question is since Vela X-1 is definitely a pulsar, why is it not accepted?
Which one has the longest spin period so far?

When this diagram is mentioned in textbooks, we do not say which kind of pulsars are included at all. Why?

$p-\dot{p}$ diagram only shows radio pulsars?  no!
you can see magnetars,radio quiet pulsars and pulsars which are only active in $\gamma-ray$

Except magnetars, there are no single pulsars only pulse in X-ray band?

If a pulsar pulses in X-ray band, that does not necessarily mean it is an X-ray pulsar?
Only pulsars in binaries and accretion-powered pulsars could be called X-ray pulsars? They should be radio-quiet?

In binaries, there are no pulsars which pulse in radio and x-ray band simultaneously?


texts: I am curious to know whether Jupiter is a reason that we have life on earth as it protects earth from comets, without Jupiter – comets would be more likely to hit us?


texts: How does a planet lose mass to its host star?

texts: How do bodies like WASP-12b lose mass to its central body? The process is never really explained in popular media, instead showing visualisations of a thin veil of gas being "sucked" in a rather straight line (and then into a ring around the star) rising straight from the surface of the planet. I highly doubt the mechanics which these illustration insinuate: Gravitation isn't working like a vacuum cleaner on a dusty rug. Either the rug goes with it, or the dust stays on the rug. The only mechanism that I can think of are particles from the upper atmosphere which happen to pick up enough thermodynamic energy so that they are faster than the escape velocity of the planet. But is this a process which effects a big enough mass transfer to be of significance? Do I overlook something? How is such a mass defect going on really?


texts: What is the physics of the "spinning dust" contribution to Cosmic Microwave Background measurements?

texts:
The lengthy paper Nine-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Final Maps and Results mentions "spinning dust" about 51 times. It is a potential contributor to the measured spectrum and the details of its emission spectrum has more than one proposed model.

question: Is there a simple way to understand the physics behind the emission spectrum of spinning dust and how it would differ from non-spinning dust?


texts: Is Rosetta changing the theory of comets?

texts:
Rosetta is now arriving at Comet 67P.

Other comets have been analyzed to some degree (Giotto, Deep Space 1, Deep Impact, etc.)

So my question is... where I can study the up-to-date theory of comets? Much of what was previously thought (eg. dirty snowball) has been discarded now, but I haven't found a good source describing the current thinking.

Are there any firm predictions that will be tested as Rosetta studies the comet up close?


texts:
The moon faces the earth with one fixed side. However there is a small vibration.

So I am not sure the south and north poles of the moon is fixed. Even if they are fixed points on the moon, the pole axis should point at different locations in the sky.

What are the general positions of the two points in equatorial coordinate system of our earth?


texts: Is energy required for gravity to have effect, or is it an energy itself?

texts: If magnetism requires some energy to exert change of motion to attract ferrous metals, then, does gravity require energy to exert attraction, or is gravity energy itself, creating attraction through centrifugal force from the earth?


texts: Gravitational waves detected are from merging of black holes few millions of light years away. While waves have reached us after travelling so far, they must have encountered many black-holes and have reached us after refracting/gravitational lens effects. Then how do one decide the correct direction of those merging black holes?


texts: What is the average temperature of all planets at 1 bar?

texts: Jupiter's (and Saturn's) "surface" temperature is defined as that at 1 bar. It is inconsistent to say the other planet's surface is their hard surface. Applying the same measure what is the equivalent standard temperature of all the IAU defined planets?


texts: What is the ratio of cosmic microwave background radiation to normal radiation?

texts: I would like to know the ratio of cosmic microwave background radiation to normal radiation in the universe.  I am considering cosmic microwave background radiation to include the microwave, and any other radiation that is being emanated from near the "edge of the universe", while normal radiation is radiation emmitted by stars, nebulae, and other sources within the universe (excluding the cosmic microwave background).  Since we are in a galaxy, I know that the normal radiation here far exceeds the cosmic microwave background, but I am interested in the "average" value over the universe.  For example: total cosmic microwave background radation in the universe / total normal radiation in the universe.


texts: What is the effect of the axial precession on the orientation of the planet's orbits?

texts:
I am working on an online application to visualize the positions of the planets and to calculate their ephemerides (you find it here, but it is not complete yet). I do not have much knowledge in astronomy and I am learning new stuff every day while developing the code. A few questions came to my mind that I hope to get answers for here.

The first thing I do not quite understand is the effect of the earth's axial precession. I understand the way it causes the vernal point to move along the ecliptic within the period of the precession of about 25770 years. But since the longitude of the ascending nodes of each planet's orbit depend on the vernal point and remain almost constant over time it seems like all the orbits change their position relative to the stars at the same rate as the vernal point does. But I cannot believe that the orientation of the orbits is related to the precession of the earth's axis.

You can see the effect in the application: When you move the topmost time slider for years you can see the zodiac rotate and the orbits staying in place because the vernal point is fixed with the scale. Shouldn't the orbits move together with the stars? But then the longitude of the ascending nodes wouldn't be constant anymore... I am confused. Thank you.


texts: Will an observer falling into a black hole be able to witness any future events in the universe outside the black hole?

texts: I know someone or something sucked into a black hole could not survive, but is the bending of light so immense that an observer falling into a black hole will be able to witness any future events in the universe? That would definitely be cool :D I have a feeling this won't work though... so could you explain in detail why? Thanks.


texts: Calculate right ascension in Zenith at this moment in my location

texts:
I've been searching on Internet about how to calculate which RA is in zenith at a given location in a given time but I haven't find anything (or maybe I don't know how to search).

Using my star finder I have not draw any conclusion.

How can I calculate which RA is on zenith on a given location in a given time?


texts: If the expansion of the universe is speeding up, how long until everything nears the speed of light, and what would happen?

texts: Since dark energy is causing everything to speed up infinitely, wouldn't everything near the speed of light? And since it's nearing the speed of light, wouldn't all kinds of strange things start happening such as time dilation?


texts: How can we explain high redshift numbers?

texts:
I just finished an introductory astrophysics course$^1$ and I have a lingering question that I can't seem to resolve.

We learned that for the first few hundred million years, the universe was pretty boring and not much interesting$^2$ happened. We also learned, correctly or not, that the first stars started forming somewhere between 500 million and 600  million years after the Big Bang.

We also learned how to use redshift values to calculate age, and we talked about how the highest $z$-number we've discovered is some galaxy (GN-z11) at roughly $z=11$.

Using this calculator, we calcultaed that this galaxy apparently formed about 410 million years after the Big Bang.

So, this galaxy seems to be older than when astrophysicists think star formation happened. How can this possibly be? Clearly one of my assumptions is wrong, so is it:

Stars actually started forming before 500 million years post-Big Bang.
Using the UCLA calculator to calculate age is technically incorrect.
A galaxy doesn't need stars to be considered a galaxy.
Some other assumption I made is wrong which makes this post invalid.

As a follow-up question, what happens if we keep finding galaxies at higher $z$-numbers? At what point do we need to reconsider our theory about what happened in the "early" universe?

$^1$I'm not an astrophysics major, so forgive any blatant falsehoods in this post.

$^2$On a macro-scale, at least.


texts: Number of stars & planets in Milky Way Galaxy?

texts: Is there any specific numbers on stars & planets count on Milky Way Galaxy ?


texts: Can the moon turn red even without an eclipse?

texts:
My friend posted a picture of the moon as if there was an eclipse because it was so red but there wasn't a scheduled eclipse at the time (it was last night, from the Philippines).

I'm a little concerned because how else is that possible? It was in Manila so I guess there was a lot of smoke in the air but I don't know if that's the reason behind the moon's redness.


texts: the most accurate system that can show the positions of planets at my birthday

texts:
My birthday : 4 December 1982

If you have such astronomical calculator on your computer please send me the result !

Alternatively if you know an online astronomical service for my purpose please link it here ?

I am so curious to discover geometrical proportions between distance and angle of planets at that date ...


texts: Questions about Hubble's brand new view of an interstellar comet (video)

texts:
This GIF is made (via giphy.com) from the new NASA Goddard video Hubble's New Image of Interstellar Object and if I understand correctly many (if not all) of these frames are from https://archive.stsci.edu/proposal_search.php?mission=hst&id=16009 (from this answer).

I have some questions about this set of images. I've plotted the start times below.

There are four groups that last about 45 minutes, each followed by a break of either 45 minutes or 90+45 minutes, is this related to the HST's orbit?
I notice a slow rotation of the star tracks over the duration of the roughly seven hours of data, it looks like roughly 20 degrees, (see GIF or the individual images) and I can't figure that out at all. Is it a rotation of the HST around its own axis?
Individual preview images (example) appear to be rhomboidal rather than square, why?


texts: Math for the "universe in a black hole" hypothesis?

texts:
There are various pop-science article entitled Are we living in a Black Hole? or Did A Black Hole Give Birth To Our Universe? which say things like

There’s a lot to like about the idea that there’s a connection between black holes and the birth of Universes, from both physical and mathematical points of view. It’s plausible that there’s a connection between the birth of our Universe and the creation of an extremely massive black hole from a Universe that existed before our own; it’s plausible that every black hole that’s been created in our Universe has given rise to a new Universe within it.

What exactly are the mathematical connections? Are those calculations in any way connected to the Black hole information paradoxon?
Background
I remember one of my professors for theoretical physics giving an evening lecture on the subject. He performed some lenghty and incredible fast calculations with chalk on blackbord. This lecture is long ago, in the age before smart phones, and I do not have records on his equations, that why I am asking here. What I do remember is that he concluded his lecture with something like "These are all convincing mathematical equations, but only once you jump into a black hole, you could see whether there are other universes there."
References

How is information preserved on the surface of a Black Hole?
New Theory Suggests We Live in a Gigantic Higher Dimensional Black Hole
Many articles refer to Prof. Nikodem Popławski in one way or the other.
Some physicists believe we're living in a giant hologram — and it's not that far-fetched


texts: When black holes such as those detected by LIGO merge, in what ways does the Schwarzschild Radius warp?

texts: I was reading the paper about LIGO's detection of gravitational waves, and I wanted to know what the Schwarzschild Radius did. For example, I feel like the simulation here is oversimplified, and that reality wouldn't actually have that simple bump together of the two radii.


texts: Potential paradox with the Big Rip and the Multiverse?

texts: I came up with this confusing theory a few years ago, but did not ask it on this site. If the Big Rip and the Multiverse theories are true, then when the Big Rip occurs, the universe's size will expand to infinity. However, the size of the Multiverse is also infinite (supposedly), and there are an infinite number of universes (also supposedly), then there is a paradox of infinities. I am still rather confused about this paradox, and is there a work-around to it, or is this completely invalid?


texts: Why is the letter *z* customarily used to denote redshift?

texts: What events led to the nearly universal acceptance of the letter "z" as the denotation of redshift? What did the letter originally stand for?


texts: Could the accelerating expansion of universe inidicate we are surrounded by "denser" space?

texts:
I'm quite novice about all this, only have read some vulgarization books and sites, but I wonder: could all the observable universe be falling outwards on some non-observable, more compact kind of barrier - I'll call it "edge"? Could this be a part of the explanation of cosmological accelerated expansion?

Like say we would be in a kind of bubble, or egg-shape thing? This thing could be inflating, and the closer matter would be from the edges, the quicker it would fall?

Good question "why would we be at the center of it?"... I know already there could be a kind of "flow" of matter at large scales which is already kind of violation of universe isotropy. Could we remove this issue with some kind gravity propagation itself?

Any sense to anybody it makes?


texts: How does the Sun orbit the Sun-Jupiter Barycenter?

texts:
I got the Orbital Elements of Jupiter around the Sun, which describe how it orbits relative to the "fix" Sun.

Jupiter
Semi Major Axis (AU): 5.20336301

Eccentricity: 0.04839266

Inclination to Ecliptic Plane (deg): 1.30530

Longitude of the Ascending Node (deg): 100.55615

Longitude of Perihelion (deg): 14.75385

Mean Anomaly at J2000.0 (deg): 19.65053

I want to convert this One-Body Problem back into the Two-Body Problem to find out where the Sun is gonna be at a given time (i couldnt find the Orbital Elemens of Sun around Sun-Jupiter Barycenter).

So the Semi-Major Axis depends on the Mass Ratio. The Eccentricity and Inclination should be equal for both, just like Longitude of the Ascending Node. The Longitude of Perihelion should be the one from Jupiter+180°, doesnt it?

The main Problem is the Mean Anomaly at J2000.0. The two Ellipses are equal, besides of the Size. Thus, the True Anomaly at a given time should be the same for Each Coordinate System. Then the eccentric Anomaly will be the same too. Does that mean the Mean Anomaly for J2000.0 will be also the same for both?

Thanks for reading and sunny greetings!!


texts: Usage of the standard solar system (astronomical) symbols

texts:
Note: this is a follow-up question based on answers I've received in TeX SE on Packages for standard solar system (astronomical) symbols on the off-chance that some here may have actual hands-on experience with both TeX and these astronomical symbols.

Recently, I have been looking for specific LaTeX packages for generating the following symbols of the solar system.

Photo source: https://solarsystem.nasa.gov/resources/680/solar-system-symbols/
I have tried using the packages mathabx and wasysym. But I have found that they both have some issues and I need to use both of them to generate the above symbols. I have discussed it on TeX SE here and got this solution:
\documentclass[a4paper,12pt]{article}

\usepackage{amsmath,amssymb}

% wasysym redefinitions
\newcommand*{\wasyfamily}{\fontencoding{U}\fontfamily{wasy}\selectfont}
\newcommand*{\astrosun}{{\odot}}
\newcommand*{\mercury}{{\text{\wasyfamily\char39}}}
\newcommand*{\venus}{{\text{\wasyfamily\char25}}}
\newcommand*{\earth}{{\oplus}}
\newcommand*{\mars}{{\text{\wasyfamily\char26}}}
\newcommand*{\jupiter}{{\text{\wasyfamily\char88}}}
\newcommand*{\saturn}{{\text{\wasyfamily\char89}}}
\newcommand*{\uranus}{{\text{\wasyfamily\char90}}}
\newcommand*{\neptune}{{\text{\wasyfamily\char91}}}
\newcommand*{\pluto}{{\text{\wasyfamily\char92}}}

% mathabx definitions
\newcommand*{\mathabxbfamily}{\fontencoding{U}\fontfamily{mathb}\selectfont}
\DeclareFontFamily{U}{mathb}{\hyphenchar\font45}
\DeclareFontShape{U}{mathb}{m}{n}{
      <5> <6> <7> <8> <9> <10> gen * mathb
      <10.95> mathb10 <12> <14.4> <17.28> <20.74> <24.88> mathb12
      }{}
\newcommand*{\Sun}{{\text{\mathabxbfamily\char"40}}}
\newcommand*{\Mercury}{{\text{\mathabxbfamily\char"41}}}
\newcommand*{\Venus}{{\text{\mathabxbfamily\char"42}}}
\newcommand*{\Earth}{{\text{\mathabxbfamily\char"43}}}
\newcommand*{\Mars}{{\text{\mathabxbfamily\char"44}}}
\newcommand*{\Jupiter}{{\text{\mathabxbfamily\char"45}}}
\newcommand*{\Saturn}{{\text{\mathabxbfamily\char"46}}}
\newcommand*{\Uranus}{{\text{\mathabxbfamily\char"47}}}
\newcommand*{\Neptune}{{\text{\mathabxbfamily\char"48}}}
\newcommand*{\Pluto}{{\text{\mathabxbfamily\char"49}}}

\newcommand*{\astrosymbolsA}{\Sun\Mercury\Venus\Earth\Mars\Jupiter\Saturn\Uranus\Neptune\Pluto}

\newcommand*{\astrosymbolsB}{\astrosun\mercury\venus\earth\mars\jupiter\saturn\uranus\neptune\pluto}

\newcommand*{\astrosymbolsC}{\Sun\Mercury\Venus\Earth\Mars\jupiter\saturn\Uranus\Neptune\pluto}

\begin{document}
\begin{align*}
   \text{mathabx: } \astrosymbolsA \\
   \text{wasysym: } \astrosymbolsB
\end{align*}
Taking \jupiter, \saturn, \pluto  \, from `wasysym' and others from `mathabx':
\begin{align*}
        \Sun\Mercury\Venus\Earth\Mars\jupiter\saturn\Uranus\Neptune\pluto
\end{align*}

\end{document}

Still, they don't exactly match the symbols of the first photo.
I guess the MWE of LaTeX codes is related to TeX SE. But I have not found any better way to cross-advertise questions of interest in multiple topics. That's why I share the codes here too.
Here in Astronomy SE, I want to know how these symbols are used in the astronomy communities/academia.

How is the frequency of using them in the technical/research publication?
How do publishers handle them when submitting articles?
Do they use any other dedicated/updated LaTeX packages available for generating these symbols?


texts:
So, this is mere musing, but it seems that stars are quite extremely far apart. I tried to determine the mean distance between nearest neighbors for stars (in just our galaxy) but I'm not sure what it is, though a first approximations I would guess that the mean is around 5 ly with some 0.5 standard deviation or so!

However, assuming I didn't screw up, the distance between two sun-massed objects required to generate 1,000N of force between them is an incredible 54.3 million ly. [Edit] If you change that to 1 billion Newtons, the distance is one galactic radius -- 54000~ ly!

I'm probably mis-estimating how much even 1kN of force would effect solar trajectories over time, but I still can't help but feel that our solar neighbors are very far away given the spheres of interaction that I would expect.

Any insights?


texts: Any ideas for an astronomy + ML project?

texts: I wish to do an astronomy related project which incorporates machine learning.Do you have any suggestions?


texts: Is it just the observable universe that is expanding?

texts:
Is it possible that it is just our observable part of the universe that is expanding, in the time that we exist, and other parts are both expanding and contracting at different rates and times?

Would light from a shrinking or slower/faster-expanding part of the universe reach us?

Could that be an alternative to the big-bang theory, in that the red-shift is a temporary situation local to our time and part of the universe? A "throbbing" energy that leads to the non-uniformity that we see in galaxy clusters; something like foam awash on the ocean surface.


texts: In the theory of multi-verses, we can imagine countless other universes where the constants of nature, including the amount of dark energy in a volume of space and possibly even shapes of hidden dimensions vary from one universe to another. Is there sound reasoning to believe that the mathematics of nature (or laws of nature) would be the same in other universes?


texts: Why Helium-burning Stars are found in a Horizontal Branch?

texts: Why Helium-burning stars are found in a horizontal branch on the H-R diagram? Why do they have roughly the same luminosity?


texts: Is the local group bound to the Virgo cluster?

texts: The virgo cluster is currently red-shifted by 0.003 according to Wikipedia; this indicates that the cluster is expanding. Will the cluster's enormous gravity eventually "win" and pull the milky way/local group back toward itself, or will our current recessional velocity combined with dark energy cause us to recede off to infinity?


texts:
I've had some discussions recently about black holes, and the issue of infalling bodies taking forever to reach the event horizon. That's essentially what Einstein said in his 1939 paper on a stationary system with spherical symmetry consisting of many gravitating masses. He said "it is easy to show that both light rays and material particles take an infinitely long time (measured in “coordinate time”) in order to reach the point r = μ/2 when originating from a point r > μ/2”.

Now, I'm a big fan of Einstein. But there seems to be two issues with this:

One is that Einstein concluded that black holes cannot form, but we
have good evidence that there are black holes out there. The obvious
example is Sagittarius A*. That's where's there’s something
with a mass 4.28 million times the Sun, with a diameter of less than
44 million kilometres, and we can't see it. Surely it's just got to be a black hole.
The other issue is that falling bodies don't slow down. Imagine you
drop a body at elevation A and it falls down to elevation B. The
"force" of gravity relates to the first derivative of gravitational
potential. Hence the bigger the difference in gravitational time
dilation between elevations A and B, the faster the body falls past
B. Then if you drop a body at elevation B it falls down to elevation
C. Again the bigger the difference in gravitational time dilation
between elevations B and C, the faster the body falls past C. In a
typical gravitational field the force of gravity at B is greater than
at A. Hence as the body descends, the acceleration increases as well as the falling speed.

Imagine a gedanken spaceship from which we've suspended a cable. We have clocks at different elevations, so we can measure the gravitational time dilation at each elevation. We can also release test bodies at each elevation and record the  clock readings as they fall past other elevations:

At the end of the experiment we can reel in the cable and upload the recorded measurements to ascertain how our test bodies behaved. My understanding is that we will always find that time dilation always increases as we descend, that the falling body always accelerate downwards, and that both the acceleration and the falling speed always increases as the body descends. Is this correct? Or do falling bodies somehow stop accelerating? And do falling bodies ever slow down?


texts: What is the maximum planet mass for human habitation? How many Gs can humans withstand on a constant basis?


texts: Great attractor is doing the big crunch?

texts:
Laniakea and other super clusters are moving towards shapely super cluster .
Even the Great Attractor is moving towards it. Isn't it all about the Big Crunch?


texts: I am interested in doing some solar spectroscopy on my own for fun. How do I go about choosing the appropriate diffraction grating?


texts: At what wavelengths can black hole Sagittarius A* be observed from Earth?

texts:
The supermassive black hole in the center of the Milky Way is blocked by dust and gas clouds as seen from where we are. Which wavelengths are blocked and which are most undisturbed for observation of Sagittarius A* and its immediate neighborhood? Does the matter between us change for example polarization at some wavelengths or cause disturbances other than blocking the light? Could galactic cosmic rays, heavy ions, from it be detected if they were emitted, or would they be deflected by magnetic fields?

By the way, at what distance from us is the most dust located? Is it concentrated in one region or are there several dust clouds in the way?


texts: Hypothetically, would we be able to see the moon from Saturn's North Pole?

texts: Hypothetically speaking, if Saturn had a solid surface that we could stand on, would we be able to see our Moon from the North Pole of Saturn? Would the rings of Saturn obstruct the view?


texts: What (actually) is the " deprojected half-light radius" of this almost-all-dark-matter Galaxy?

texts:
The recent news of the Ultra Diffuse Galaxy (UDG) Dragonfly 44 is an excellent example of what could be termed 'observe different' thinking. The dragonfly telescope is noted not for the size of its collective aperture, but for the absence of the diffracting effects of secondary mirrors and surface roughness that limit the contrast of dim objects in conventional telescopes when brighter sources are nearby. See here and here and here.

above: image of a Dragonfly refractive array telescope from here. Image: P. Van Dokkum; R. Abraham; J. Brodie

above: The Dragonfly 44 ultradiffuse galaxy from here. "Dragonfly 44 is very faint for its mass and consists almost entirely of dark matter. (Pieter van Dokkum, Roberto Abraham, Gemini Observatory/AURA)"

Once identified, the radial velocities of the stars in Dragonfly 44 were measured using DEIMOS on the Keck II telescope, in order to determine a value for the mass for the dim, ultra-diffuse galaxy.

I started reading the ArXiv article but quicky got bogged down in the abstract. The very exciting result is that the luminosity and therefore total number of stars is much smaller than what one would expect from the mass obtained from the radial velocity measurements, suggesting that it is made almost entirely of dark matter. I wanted to see if I could understand how the mass was calculated, but I got stuck on the phrase deprojected half-light radius.

Could someone just outline how this calculation is done, and what that phrase actually means?

  Recently a population of large, very low surface brightness, spheroidal galaxies was identified in the Coma cluster. The apparent survival of these Ultra Diffuse Galaxies (UDGs) in a rich cluster suggests that they have very high masses. Here we present the stellar kinematics of Dragonfly 44, one of the largest Coma UDGs, using a 33.5 hr integration with DEIMOS on the Keck II telescope. We find a velocity dispersion of 47 km/s, which implies a dynamical mass of M_dyn=0.7x10^10 M_sun within its deprojected half-light radius (my emphasis) of r_1/2=4.6 kpc. The mass-to-light ratio is M/L=48 M_sun/L_sun, and the dark matter fraction is 98 percent within the half-light radius. The high mass of Dragonfly 44 is accompanied by a large globular cluster population. From deep Gemini imaging taken in 0.4" seeing we infer that Dragonfly 44 has 94 globular clusters, similar to the counts for other galaxies in this mass range. Our results add to other recent evidence that many UDGs are "failed" galaxies, with the sizes, dark matter content, and globular cluster systems of much more luminous objects. We estimate the total dark halo mass of Dragonfly 44 by comparing the amount of dark matter within r=4.6 kpc to enclosed mass profiles of NFW halos. The enclosed mass suggests a total mass of ~10^12 M_sun, similar to the mass of the Milky Way. The existence of nearly-dark objects with this mass is unexpected, as galaxy formation is thought to be maximally-efficient in this regime.


texts:
I have read various discussions of the Julian day, including that on the Wikipedia, but none of these appear to define the maximum Julian day or proleptic Gregorian year in which that maximum day would occur.

Is there a maximum Julian day? If so, what is it?


texts: What is this rapidly twinkling red, blue, and white star I saw?

texts:
Last night, I was on my balcony at 1AM (PST) and I looked up and saw two stars near the horizon (I'd guess ~30 degrees above the horizon), and they were "twinkling" about twice as fast as other stars higher in the sky, and I could clearly see them changing from red to white to blue repeatedly. Other stars in the sky only appeared white to me, and didn't seem to "twinkle" as rapidly as these two stars did. The red and blue make me think of red-shift and blue-shift, but I don't know how I would see both from the same object.

What was I seeing?

I don't know if it helps, but I am in the Los Angeles area, and I was looking in a roughly north direction. almost exactly to the east, according to google maps.

Edit: I tried taking a picture, but light pollution from the nearby street lights wouldn't permit me taking a decent picture. However, I noticed a group of three stars close together in nearly a perfect almost vertical line, and managed to find that in Stellarium. I think I found the two stars I am seeing: Procyon and Sirius

Is there anything about either of these stars that would make them show as red/blue?


texts: Is the difference between LIGO & Virgo and their "Advanced" versions really generational, or were these just planned incremental upgrades?

texts:
I just learned the term "third generation gravitational wave detector" in answers to What would a kHz gravitational wave detector look like? (mountains on millisecond magnetars) How would it differ from LIGO/Virgo?
Wikipedia's Gravitational wave observatory; Interferometers lists LIGO and Virgo as 1st generation, and Advanced LIGO and Advanced Virgo as second generation.
Is the difference between the originals and the "Advanced" versions really generational or were these just planned incremental upgrades that were just waiting for funding once the basic systems had demonstrated they worked as planned?


texts: Requirements for an amplifier and filter for a horn antenna-based 21 cm radio telescope?

texts:
We are looking into the possibility of building a low budget horn antenna for detecting 21 cm hydrogen line radiation (~1420 MHz) and and possibly measuring its spectrum.

What are the types of parameters and specifications we should look for in an amplifier and filter that would be connected to the input dipole at the end of the horn?


texts: What would happen if a rocket traveling at speed of light would collide with a planet (like earth)?

texts:
Let's assume it is possible for a spacecraft to travel at the speed of light (I've read the interstellar book by Kip Thorne, apparently this is theoretically possible if you swing around two black holes)

I have watched the video where the traveling of a light particle is simulated and while planets are certainly big enough so you can adjust your route, what would happen if a rocket (or spaceship in general) would collide with an earth-like planet (i.e. a planet having a massive surface). Would we burst through the whole planet, make it only to a core, or just a few km? I know what happens when a meteor lands, but obviously they aren't traveling at the speed of light.

And one similar another question - when a spaceship is traveling at the speed of light, is there a problem with collision with smaller objects? I think you can't avoid millions of rockets in outer space, it would surely damage the spaceship, wouldn't it?


texts: Is it possible for there to be a dense enough nebula to form stars outside of any galaxy? Does a galaxy have a minimum size to produce stars? Or could you have a few dozen stars clustered together by themselves?


texts: Are planet-destroying quakes possible or observable?

texts:
The Gutenberg-Richter-Law is a very-well studied relationship between the magnitude and total number of (earth)quakes. In theory, there is no upper bound for the size of a quake other than the size of the planet. In other words: There is a non-zero probability (which is rather low) that a quake can rip appart the whole planet. There are numerical evidences with toy models such as the Olami–Feder–Christensen model suggest, such things can really happen.
Therefore my question: Are they any hints for (exo)planet-destroying quakes? And what about star-quakes which occur during stationary phases of star evolution?
References

cond-mat/0608324: Transient and stationary behavior of the Olami-Feder-Christensen earthquake model - not the publication which claims that planet-destroying quakes are possible, but a possible introduction to the kind of numerical methods used


texts: In which direction is the sun travelling?

texts:
Relative to this simple drawing, can someone explain to me,

in which direction is the sun and its solar system travelling,
which star (irrespective of distance) is closest to that direction,
and in which direction the milky way center is.


texts: How can I convert Bayer/Flamsteed designations to Hipparchos numbers?

texts: In a text file I have a table of star data with Bayer/Flamsteed designations. I need to convert these into Hipparchos numbers. How can I automatically do this?


texts: Is there a standard definition for $\eta$ and $\xi$ in terms of Ra and Dec, as used in an astronomical coordinate system? I'm used to working with Ra and Dec, and am not sure how to precisely interpret this spatial graph from de Boer et al. 2013.


texts:
The redshift-distance relation is $cz=H_0d$. So if we have $z$ we can calculate $d$. But is there a way to calculate or covert or write this $d$ in terms of right ascension (RA) and declination (DEC) ?

Thanks in advance


texts: Minkowski 92 is a protoplanetary nebula. But after which Minkowski is it named? Same question for Minkowski's object (part of NGC 541).


texts: Having some weird issues with my tracking (Advanced VX)

texts:
I need your help! I am having some weird tracking issues with my tripod (Advanced VX). When I setup and calibrated my scope yesterday I took this picture of NGC6888 (90s exposure):
As you can see this image looks quite good tracking wise.

However due to unknown reasons it seems that 1 in 3 images is always bad and has tracking issues, like this one:
This movement always occours in the same direction, it seems that for some reason one axis of the mount is moving faster periodically, causing these tracking issues.

Funny is that is seems to be occouring periodically. I always get 4 images good, 2 images bad, 4 images good, 2 images bad, ...

I tried fiddeling around with the anti-backlash settings (I never touched them before) but that didnt fix it. My current anti-backlash settings are: RA +- 55, Dec +- 60

Does anyone know where those tracking issues could come from and how to fix them? Note I also have a 5s mirror-lock so it should not come from vibrations of the camera.


texts: Can the Gaia telescope detect small temporarily captured asteroids near its Lagrange orbit?

texts:
The Gaia space telescope is in a Lissajous orbit around the Sun-Earth Lagrange point 2. The orbit period is about 180 days and the size of the orbit is 263,000 x 707,000 x 370,000 km. It has been theoretically concluded that there should be a population of temporarily captured orbiters (TCO's) around that Lagrange point. All but a handful of them should be less than a meter in diameter and too small to be observed from Earth. Only one TCO, 2006 RH120, has ever been observed, a 5 meter diameter one.

Since Gaia will be in a somewhat similar orbit as the TCO's and will scan the entire sky several times over the coming years, and an IR telescope is sensitive to asteroids, I wonder if it will be able to detect such TCO's. And if so, what could we find out about them? Gaia will not track any asteroids nearby, if it catches the same TCO more than once it would be by chance, I suppose. Could Gaia learn about their sizes, orbits, surface compositions?


texts: How does the black hole at the center of M87 look like in the visible spectrum?

texts: I learned here that the picture of the black hole we saw all over the news was a false color image, based on the radio spectrum emissions. How would the black hole at the center of M87 look like when seen by the naked eye from a close enough distance, or by a large enough optical telescope? (please tell me if the two would be different)


texts: How was an infrared picture of the entire universe taken?

texts:
(click to enlarge)

How was this picture of the supposed entire universe taken in infrared? Also, why does it seem as though almost all of the matter is in a line formation over the center? It makes sense why most matter would be concentrated in the center, but why is it in a line?


texts: What is the detector size of LANDSAT 8's detector array?

texts:
According to the suggested tags, this must be the right forum:
I found  that for each band of Landsat 8 over 7000 detectors are on the array. Does anyone know how big each of the sensors is?


texts: What distance is considered 'close' for the 9th nearest neighbor of a galaxy?

texts: I am currently working on determining the nth nearest neighbors of a large survey of galaxies. I am not an astronomer by trade, so I am unsure of interpreting some of my results. I have discovered for the sample of galaxies their 9th nearest neighbor distances. It turns out the mode of this distribution by far is between 2mpc and 3mpc. Since I am unsure of the scale of these implications I would prefer if a well versed astrophysicist can tell me if the distance to the 9th nearest neighbor galaxy of 2-3mpc would be considered densely clustered. These galaxies are at intermediate redshift.


texts: Are many exoplanets synchronously tidally locked like Mercury?

texts:
The only tidally locked planet in the Solar system is Mercury. But it is synchronously tidally locked 3:2, because of the relatively high eccentricity of its orbit, so doesn't turn the same side towards the Sun. I wonder if this is common for exoplanets?

Many discovered exoplanets are close to their star and must be tidally locked. Has any of them been determined to be synchronously tidally locked, like Mercury? Is Mercury a rare freak in this respect, or a representant of a common phenomenon?


texts: How much mass would have to be added to the Sun to significantly alter any of its characteristics?

texts:
While this might at first sound like an XKCD What If? question, let's proceed with it because astronomical objects do occasionally merge.
How much mass would have to be added to the Sun to significantly alter its characteristics (lifetime, spectral type, size, etc.)?

As an example, from Wikipedia's Rogue planet:

A rogue planet (also termed an interstellar planet, nomad planet, free-floating planet, unbound planet, orphan planet, wandering planet, starless planet, or sunless planet) is a planetary-mass object that does not orbit a star directly. Such objects have been ejected from the planetary system in which they formed or have never been gravitationally bound to any star or brown dwarf. The Milky Way alone may have billions to trillions of rogue planets, a range which the upcoming Nancy Grace Roman Space Telescope will likely be able to narrow down.

...if one doesn't fall into the Sun first!
Just in the last few years alone we've seen both a comet and an asteroid with extra-solar velocities enter the inner solar system, compare that to the 4.6 billion year age of the Sun.

2I/Borisov 2.01 AU perihelion
ʻOumuamua 0.255 AU perihelion


texts: Do we know the fluctuations and constant temperature depth of the moon?

texts:
Disclaimer: I have no formal scientific training.

From what I understand, surface temperature effects on Earth extend only so far into the ground so that at a certain depth the temperature remains constant around the globe.

Has any attempt been made to identify/predict subsurface temperature fluctuations and/or constant temperature depth?

Note: The reason I am interested in looking under that particular rock, so to speak is that given the dark side/light side temperature difference on the moon I am wondering if we can predict the ideal location and depth on the moon to find a shallow surface layer that leads to a constant temperature in a range suitable for human/plant life without requiring machinery to preserve the temperature.

Related:

https://www.physicsforums.com/threads/temperature-for-3-or-4ft-underground.826193/


texts: Is time taken into account by astronomers when creating and using maps of the universe?

texts:
There's really two questions I'm asking.

Firstly, when maps are produced of stars and galaxies, are they just produced as we see them now from our viewpoint? Or are they based on the motion of those bodies? Eg Galaxy X is 1 million light years away and we know it's moving at Y speed, so it's real position now is actually 1 million years worth of movement along that trajectory.

Secondly, are those things taken into account when doing other studies of things like dark matter? Ie things are actually further apart than what we see because we're seeing them as they were Z million years ago. I would expect that would affect calculations for things like how much 'missing' matter there was.

To try to further clarify this second question, simplifying things to 3 points on a triangle... if we're at A and we observe points B and C which are X billion light years apart, then the effect of gravity on the speed of B and C moving apart would have been greater in the past when they were closer together and furthermore the effects of the current gravitational force will take more than X billion years to reach the other object. As far as I understand, dark matter is a way to account for observed gravitational effects that can't be accounted for in other ways. When astronomers do these calculations, can I assume that they have taken into account the time delay in the effects of gravity between galaxies? Or have I in my naivety, stumbled on some profound insight! (I doubt it.)


texts: Looking for methods to preserve night vision

texts:
Does anyone have a method to preserve night vision so that a car or other passing light source does not ruin it?
I have a dark location to observe the sky; however, it is near a rarely used dirt road.  I can hear a car coming in time to protect my night vision, but have been unable to find a method so that its light does not ruin my light vision.   I have tried putting a 5-gallon metal bucket over my head, covering my eyes with a towel, etc.   My night vision still gets ruined.
I want to be able to totally block all light from my eyes until the car/light-source passes.


texts: Can objects enter hydrostatic equillibrium through processes other than the influence of gravity?

texts: Wouldn't a droplet of liquid (say water) floating around in space become spherical and "in hydrostatic equilibrium" due to surface tension but not gravity?


texts: Eyepiece diameter for small focal length planetary viewing on a large dobsonian?

texts:
I have a 12" dobsonian with a 1500mm focal length and want to do some higher magnification planetary viewing. Currently my highest magnification is ~80x via my 19mm eyepiece (calculated here), but I would like to do some viewing at higher magnification.

My telescope is fitted for 2" diameter eyepieces, but I have an adapter for  1¼" eyepieces as well. I'm seeing a plethora of affordable 1¼-inch 9mm eyepieces, but very few 2" diameter options and very pricey at that.

At this point, I see the following options, by increasing price:

1¼" diameter 9mm eyepiece
3x Barlow lens
2" diameter 9mm eyepiece

I've read that the 2" eyepieces yield greater field of view advantages. Is that still true when the goal is a narrow focal length on solar system objects?

Would using a Barlow lens on my existing 2" eyepieces retain this advantage in a meaningful way?

In summary, is there any significant value in keeping to the 2" diameter eyepiece capability of my telescope when doing planetary viewing with low focal length given the magnitude of the cost difference?

I've referenced a "9mm" eyepiece here merely as an example, I'm sure most anything in the 5mm-12mm range would be fine.


texts: What's that very bright star (south-oriented, appearing at 5 p.m.)?

texts:
From my home I can see a very bright star (or a planet ?), appearing before 5pm local time, when I look toward South. It's really much more brighter than any other star, it's very often the only one you can see because of ambient light in the neighbourhood. It's even visible when it's a little bit cloudy.

Details:

My Location: N 50° 43.640' E 005° 41.430' (East of Belgium)
Time : 5pm (4pm UTC), December 21st, 2016
Direction : Almost straight on South (190°)
Altitude : 35°

Note that angles are rough estimates.

So, what's that star ?


texts: Are galaxies moving away with constant acceleration?

texts: Suppose that we could measure the current acceleration with respect to us of a distant galaxy chosen at random in our observable universe (Ignore the peculiar motion of the galaxy). Is the acceleration constant, is it increasing or is it decreasing?


texts: What are the present, and potentially the future roles of data scientists in Astronomy?

texts: I am a data scientist and curious about their roles in modern Astronomy, both now, and in the near future. What are type of roles and projects where data scientist are most active in Astronomy? What are the basic solutions provided by data scientists in astronomy. Are there data scientists as principle investigators, or are they at least team members in research efforts?


texts: Can gravity be amplified by other celestial bodies in its vicinity?

texts: I`m wondering if the gravitational pull from earth that should be constant around the planet, will get amplified by a celestial body like the moon orbiting the earth?


texts:
Given two bodies of equal mass in an elliptical orbit:

I know they will be orbiting about a common center of mass, i.e. the barycenter. But, do the velocities have to be equal in magnitude and opposite in direction (normal to R when R is their distance from each other) for the orbit to be stable? I think, if the velocity of one mass were to vary with respect to the other it would create a moving barycenter in which the two masses would collide or throw on another out of the orbit, but I can't find any mathematical verification of this.


texts: Does the edge of the Universe travel faster than the speed of light?

texts: The Universe is expanding faster than the speed of light then does that mean matter at the edge of the universe is also traveling at the speed of light or are ether opposite sides of the universe are expanding over half the speed of light equaling more than the speed of light ? Looking from outside of the universe to the nearest edge would light proceed slower or faster combined with the speed of matter traveling on the edge of the universe?


texts: Conceptual Doubt regarding the calculation of the Solar Constant

texts:
The Solar constant is the intensity of the solar radiation in the
  upper atmosphere. It's value is about $1400$ $Wm^{-2}$.

Now we begin by stating that the Power radiated by the sun is about $3.9*10^{26}$W. Then we using the Formula $I=\frac{P}{4\pi d^2}$, we compute the Intensity. (Here d is $1.5*10^{11}$m).

I understand the mathematics but have trouble in interpreting the meaning of the solar constant. The Intensity formula used above is generally depicted by authors as follows (as per my understanding): There is a sphere around the Sun of radius $d$ and if the power is radiated equally in all directions then each point on the Sphere receives an Intensity $I=\frac{P}{4\pi d^2}$. But the Earth is not a point object, so is this assumption valid?

Next, what do you mean by the upper atmosphere? I've come across another version:

  The Solar constant is the intensity of the solar radiation in when the sun is directly overhead. It's value is about $1400$ $Wm^{-2}$.

I guess my confusion is due to a lack of an intuitive understanding of this concept and I would be grateful if anyone could provide me with one.


texts: Did Gaia actually generate complete light curves for 212 Cepheids in other galaxies?

texts:
The recent BBC news item Gaia clocks speedy cosmic expansion says that a recent Gaia measurement of 212 Cepheid variables in other galaxies within the local group yields a Hubble constant of ~73 km/s/Mpc which is in agreement with a previous measurement using the Hubble telescope.

The results are reported in: A test of Gaia Data Release 1 parallaxes: implications for the local distance scale. I have included Figure 1 at the end here. If I understand correctly, the x-axis or "Photometric Parallax" represents photometric data which is compared to a model to yield a distance, which is then expressed as an equivalent parallax.

Gaia is not a "point and shoot" instrument like the Hubble telescope. It has a slow, extremely steady rotation in order to scan at least 1.5 full revolutions - enough for every start in the scan to pass completely across the CCD array through both telescopes.

But this isn't an optimal observing plan for collecting data on a group of Cepheids. Although there are similarities, the light curves of different stars will be distinct. Am I naive to think that it is necessary to build up a nice, complete light curve with dense points in time in order to use the photometry for precision distance calculations? Was this actually done within Gaia's survey observing program, or was there a special observing plan for the Cepheid measurements?

The data also needs to be good enough to calculate the periods of each star with sufficient precision. The curve of absolute magnitude vs period is quite steep at low periods, meaning the error in the calculated distance is strongly affected by an error in the period.

And could someone help me understand - what is a TGAS parallax?

above: Figure 1 from here.

above X2: "Figure 4 and 4a: Cepheid light curves (click on images for larger versions) Light curves for the twelve Cepheid variables in M100 that have been observed with Hubble. The absolute magnitude, M, is determined from the period of the Cepheids. Adapted from Freedman et al. (1994)." from the tutorial: https://astrosociety.org/edu/publications/tnl/57/realastro3.html


texts: "Mysterious radio signals" - how could a geostationary satellite and Ross-128 line up with Arecibo?

texts:
The Phys.org article 'Mystery' signal from space is solved. It's not aliens cites a summary of the conclusion "by Abel Mendez, director of the Planetary Habitability Laboratory at the University of Puerto Rico at Arecibo in a blog post Friday, revealing the true nature of the signals."

After further fueling speculation by summoning the world experts in the hunt for life elsewhere in the universe—The SETI Berkeley Research Center at the University of California—the team issued its conclusion.
"We are now confident about the source of the Weird! Signal," Mendez wrote.
"The best explanation is that the signals are transmissions from one or more geostationary satellites."
The signals only appeared around Ross 128 because it is located "close to the celestial equator where many geostationary satellites are placed," Mendez added.

The article also goes on to say:

Astronomers detected strange signals that seemed to be coming from a dwarf star about 11 light-years away, but have now determiend that the signals are interference from a distant geostationary satellite

Mendez is further quoted the Space.com article Weird Radio Signals Detected from Nearby Red Dwarf Star:

Each of these hypotheses has its issues, he said. For example, solar flares of the type that could be responsible generally occur at lower frequencies. In addition, Mendez wrote, there aren't a lot of other objects in the Ross 128 field of view, "and we have never seen satellites emit bursts like that."

and in the Space.com article Not Aliens: Weird Radio Signal from Star Likely Has Duller Explanation:

"This explains why the signals were within the satellite’s frequencies and only appeared and persisted in Ross 128; the star is close to the celestial equator, where many geostationary satellites are placed," Mendez added. "This fact, though, does not yet explain the strong dispersion-like features of the signals (diagonal lines in the figure); however, it is possible that multiple reflections caused these distortions, but we will need more time to explore this and other possibilities."

Wikipedia lists the star Ross 128 at at declination of about +0° 48', and the latitude of the Arecibo telescope to be about +18° 21'. Satellites in geostationary orbits are in a circular ring approximately coincident with the equator at a distance from the center of the Earth of only about 42,000 km. From the Northern hemisphere, geostationary satellites will appear several degrees south in declination. (See this interesting answer.)
For Arecibo, I calculate about -3.2° declination.
QUESTION: How could a radio telescope have picked up satellite signals from a satellite at about -3.2° declination while observing a star at +0.8° declination? And why wasn't this immediately ruled out - surely radio telescopists know about satellites by now, especially the crowded ring of geostationary satellites! Aren't there standard procedures to rule these out before making announcements?
Could the half-angle acceptance really have been 4 degrees? Since the brown red dwarf is extremely close to the solar system, could proper motion put it 4 degrees away from the value listed in Wikipedia?

above: "The signal that seemed to emanate from the red dwarf star Ross 128, as detected by the Arecibo Observatory in May 2017 (enclosed in the red frame)." Credit: PHL @ UPR Arecibo  From here.


texts: Open source code for the maths behind a heliostat?

texts:
Theoretically, using a Raspberry Pi, (at least) one mirror, and two motors, one should be able to build a heliostat, i.e. a device which redirects sunlight to a fixed spot, like a scrub in the shadow of a building.
I am now searching for heliostat (open) source code, ideally in python, hopefully with enough comments. Also: Is my following rough approach correct?

We need to know the exact geographical location of the mirror in terms of longitude, latitude. For simplicity, we assume that the mirror itself always has an obstacle-free view of the sun.
For a given time, we can use celestrial mechanics to calculate the path of the sun on the sky.
Using the reflection law from geometrical optics, we can determine the position of the mirror, since we know the vector from the mirror position to the spot we want to direct light to.

That sound simple enough, at least theoretically. I read that for step 2, many use precalculated tables. Why? Is it numerically so challenging?
References

https://www.sunearthtools.com/dp/tools/pos_sun.php
Jon Henley: Rjukan sun: the Norwegian town that does it with mirrors
Renard Bleu: ICARUS: the Analog Heliostat
Raspberry Forum: 2 axis Heliostat
Open Source Sun Tracking Skylight
Sadly mostly offline, but everybody is linking there: http://www.cerebralmeltdown.com/


texts: Calculating AZ and ALT from RA and DEC: values are slightly different from Stellarium


texts: Is this star group a constellation recognized by the IAU?

texts: Below is an arrangement of stars I've found in a TV series. As an amateur astronomer I cannot identify if this is a constellation, after having looked through what is recognized by the IAU. Is this just a depiction of a random group of stars?


texts:
Is there a physical limit to how far we can go?  I am thinking there could be based on the following:

1: There are parts of the universe expanding faster than the speed of light that we will never be able to get to (without faster than light travel)

2: There are a finite number of galaxies between here and the distance where 1 takes place.

3: If we travel even at the speed of light, it seems we would at some point pass that finite number of galaxies, and wouled not be able to reach the next one!

Does this mean there is a limit to how far we can go, and furthermore, we will experience the “big rip”?


texts: Adaptive Optics Shack-Hartmann Sensor and Deformable Mirror

texts:
I have a technical question regarding the Shack-Hartmann sensor in deformable mirrors.  What algorithm is used to take the Shack-Hartmann measurements of local tilt and turn them into a full phase estimate that can be passed to the  deformable mirror?

(Source: Wikipedia1)

I see that the the sensor itself can generate an estimate of the derivative of the wavefront $w(x,y)$ by observing the offset of the centroid of the guidestar. If the delta in from center of the guidestar is $\delta_x$ and $\delta_y$ then the derivative of the wavefront in that region is proportional $\delta$:

$\frac{dw}{dx} \propto \delta_x $ and $\frac{dw}{dy} \propto \delta_y $

Geary's Introduction to wavefront sensors2 has the following diagram:

with the comment: "To reconstruct the wavefront, the local tilts must be
stitched together".

Is it enough to connect them end-to-end, perhaps make them non-negative, and pass them on? The values transmitted are usually Zernike Polynomial modes, so do we we desire to make them positive or zero mean? What algorithm is actually used to take the Shack-Hartmann measurements of local tilt and turn them into a full phase estimate that can be passed to the deformable mirror?

1 By 2pem - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=15279624

2 Geary, Joseph M.. (1995). Introduction to Wavefront Sensors.


texts: Just out of curiosity. What's this curvature per unit length for a sphere? I see a lot of flat earthers using it.

texts: I've seen most flat earthers mention if earth was a sphere the earth should curve at x value per unit length. Is that even a proper logic? Radius of curvature is constant for sphere and a circle of a particular radius. If that logic exist can anyone share a simple diagram? I just can't comprehend how they got to that logic. Thanks in advance.


texts: Why is our heliosphere an asymmetric croissant shape?

texts:
The big, recent astronomy news about our heliosphere's asymmetric croissant shape has me confused....
Some articles mention the influence on our solar system's outermost boundary of very hot cations, and since positive charges are affected differently by magnetic fields than negative ones, maybe this is the reason....
Or maybe we live in a weird part of the Galaxy?
Perhaps no one knows yet, and I'm getting too excited here.....


texts: From which country or area is the new moon visible first?

texts: Being able to see the Moon is dependant on various factors like sunset timing etc. Considering all these factors, which country or area of the world sees the new moon first? I am asking about the new moon.


texts: What does "forward facing" mean for space telescopes?

texts:
I just noticed this announcement from the K2 mission that the field observed for Campaign 16 of the K2 mission would be changed so that the telescope would be "forward facing", saying that "observing in this mode allows for simultaneous observations from K2 and from Earth."

(an aside: Campaign 17 was originally planned to be a forward facing to facilitate supernova science, but it was discovered that the telescope may not have enough fuel to last through Campaign 17, hence the modification to Campaign 16 to still facilitate supernova science)

What exactly does it mean to be forward facing?


texts: Tracking a heliographic coordinate on CCD

texts:
Given the latitude and longitude of a heliographic coordinate, I want to place the point on a CCD image and simulate its motion for a particular duration. Though I am able to track the motion of a point on the Sun, I am unable to place the point at the exact location.

For example, (0,90) should ideally be placed at the right edge of the Sun, but with the current code, it falls outside the image. The issue seems to be in scaling.

Can you please suggest the parameters that I need to take into account while scaling.I have included the plate scale of the CCD, the ratio of the radius of the Sun to the Earth-Sun distance.

The code:

%% plate scale,pixel size = 0.6 arcseconds/pixel
p = 1/0.6

%% Radius of the Sun/Earth-Sun distance
a = 0.0046491838

%% scaling factor, converting it to degrees
s = a*p*3600

%% Central pixels
xC = 2048;
yC = 2048;

%% latitude and longitude
l = 0
b = -90

x = round((b*s*cos((l*pi)/180))+xC)
y = round((l*s)+yC)

--> x =-463 & y = 2048 and hence the point is not getting plotted.


texts: Are there expanding-universe cosmological models that do not include inflation?

texts:
I'm happy that the universe is expanding, because we have good scientific evidence in the form of galactic redshift. The Wikipedia Hubble's law article gives what I think is a fair explanation of that. It redirects from cosmological redshift and maybe gives too much emphasis to Doppler shift, but no matter. Because like I said I'm happy that the universe is expanding. Even if there was no evidence, my understanding of general relativity would be telling me that the universe just has to expand. For the life of me, I still don't know why Einstein didn't predict it.

But what I'm not happy about is inflation. I take note of articles like Physicist Slams Cosmic Theory He Helped Conceive where Paul Steinhardt is critical of inflation. He says things like this:

  "The whole point of inflation was to get rid of fine-tuning – to explain features of the original big bang model that must be fine-tuned to match observations. The fact that we had to introduce one fine-tuning to remove another was worrisome. This problem has never been resolved".

I empathize. I don't empathize with his cyclic universe, but I share his view that we have not explained any feature of the universe by introducing inflation. In fact, I would dispute the claims that inflation explains why the universe is isotropic, homogeneous, flat, and bereft of magnetic monopoles. I'd even say that I think inflation is a solution to a problem that doesn't exist. But as the Wikipedia article says:

  "The basic inflationary paradigm is accepted by most scientists, who believe a number of predictions have been confirmed by observation;

I don't. I'm just some IT guy, but I'm like "the substantial minority of scientists who dissent from this position". Steinhardt is mentioned, as are John Earman and Jesus Mosterin. I can read their paper on SciHub. But what I'm struggling to find is any big-bang cosmological model or models that don't feature inflation. It seems to be included in all big bang literature and images, including this "wine flute" public domain image courtesy of NASA:

Can anybody point some out to me? In other words my question is this:

Are there expanding-universe cosmological models that do not feature inflation?


texts: How to calculate the limb darkening $\mu$ value

texts:
I am reading about limb darkening and I am very confused how to find the value of $\mu$.
It states it can be found by $\mu = \cos(\gamma)$, but I am lost how $\gamma$ is found, or what it represents.
If a planet is, say in mid-transit, would $\gamma$ be zero degrees?
I can't seem to visualise the trigonometry to understand it. Hope someone can explain.


texts:
Fast-moving objects near our earth have different paths in the sky. They are different with stars far away.

For telescopes, when we do not know an object's orbit, catching up with its orbit and not losing it is a problem ? How to figure out a new object's orbit parameters quickly before we lose it? For an old object with an irregular orbit, can a telescope track it?

The typical speed in the asteroid belt may be smaller than 1"/min? But there may be faster objects. Then the paths are not so simple and regular.


texts: Strength of core-envelope coupling in stars

texts:
For a star with a given Zero-Age Main Sequence (ZAMS) mass, as a function of metallicity how strongly is the star's core coupled to its envelope?

I understand that the core-envelope boundary is only (semi-) well defined for Main Sequence stars that do have a core, and that in principle the final spin (angular velocity) of the core should depend on the spin of the star prior to losing its envelope in a mass transfer event. I've read, here for instance, that the core should be nearly completely uncoupled from the envelope, however in this recent paper they assume that the coupling is sufficient enough to determine the natal spin of the stellar core (see figure 1).

Is there a simple way to understand the strength of core-envelope coupling in terms of the ZAMS quantities of the star, without performing full stellar population synthesis?

I asked this question at the Physics SE but it has received very little interest.


texts: Selecting a Telescope for Viewing Planets

texts:
I hope to observe planets like Jupiter and Saturn, and moons. I am a novice when it comes to telescopes and I know images in magazines are not taken with at least 12-inch telescope in a middle of nowhere. Is it possible to view Saturn in little yellowish and Mars in little reddish using following telescopes?  I am going to buy one of them. Which one is worth more for the money with the price difference?

I am living in Sri Lanka (a country close to the equator) in a suburban city.

Option 1
EQ-Reflecting telescope

Aperture: 135mm
Focal length: 800mm Focal ratio: f/6
Max power: 265x when the air is steady
Price: 300USD approx
Link: http://www.ksonoptics.com:8081/Product/PrdDtls/121/

Option 2
EQ-Reflecting telescope

Aperture: 114mm
Focal length: 900mm Focal ratio: f/8
Max Power: 228x when the air is steady.
Price: 220USD approx
Link: http://www.ksonoptics.com:8081/Product/PrdDtls/119/


texts:
I live in north India. About 24° latitude. I can see a very Bright star in sky. Its towards east and high up. Is it Venus , Jupiter, star or anything else?

Its not Sirius. I used Orion belt for that.

Date: 24 March , 2016

Time : 8 :00 p.m.

At 11: 00 pm.
Its directly upwards. Angle b/w moon and sun ~60°.


texts: What are the objects that are visible from a city?

texts:
I live in a light polluted city of the northern hemisphere and I would like to know what I can see with my Skywatcher BK 707AZ2. I have already seen Jupiter (and its moons), Saturn, Mars, M45, the Double cluster, M42 and, obviously, the Moon.

M31, M13 and maybe M33 are also probably visible, but what else?


texts: Table of dates for planet retrograde motion

texts: Is there a table which shows the dates of the planets retrograde motion? I want to know at which date a certain planet will start the retrograde motion.


texts: How do you define the diameter of the Sun

texts: That is, it's twice the radius where the radius is from the centre of the sun to some edge. But what is that edge?


texts:
I was introduced to mean free path in my astro physics class,
and the professor posts a question for us to ponder: "Why do we need the "mean" in mean free path?"

This further makes me to wonder what is the mean free path for, and how is it used?


texts: How do we know that the mass ratio of hydrogen and helium in the sun is approximately 3:1?

texts:
From what I learnt, we can find what elements are in the sun by analysing spectrums since each elements has same emission spectrum, and when you look at the sun's spectrum, you can see absorption spectrum missing some lines which is the elements.

But how do we know how much are there? Are there other ways to find out how much of each elements contributes to the sun?

And how can this become an evidence of Big Bang?

Are these even correct?

(Can you explain it easily)


texts:
I have only recently started to study astronomy. I would like to ask if I want to get the angle of Mpc under different redshifts, but the result I calculated seems a bit strange. Did I make a mistake while converting?
from astropy.cosmology import FlatLambdaCDM
import numpy as np
from astropy import units as u
import math
cosmo = FlatLambdaCDM(H0=70, Om0=0.3)

d_A = cosmo.angular_diameter_distance(z=0.3)
print(d_A) #  Mpc

x = 3.29*u.Mpc

theta = (x/d_A *(180/math.pi) *(1/3600))
theta = theta*u.arcsec

print(theta)


texts: When the magnetic poles of the earth get reversed, does the earth keep on revolving in the same direction or does it start revolving in the opposite direction?